1. Field of the Invention
The invention relates to a method and an apparatus for positioning a feeder needle, and to a feeder comprising this needle; the invention also relates to a production line for optical components.
2. Description of Related Art
Feeders which have been disclosed hitherto, in particular needle feeders, have long been used for portioning, for example, heated and liquefied glass, and usually have a portioning accuracy of ±3 grams.
Nowadays, however, even higher portioning accuracies are required for the production of glass engineering items, such as for example gobs for lens manufacture or for the manufacture of optical components.
Patent Abstracts of Japan 11-157847 relating to a “Device and method for supplying molten glass” disclose the accurate positioning of a feeder needle with spring assistance. However, one drawback of this holding means is that due to the fixed spring forces either positioning can only be carried out slowly to avoid mechanical damage to the feeder needle seat, or high levels of wear to the valve have to be accepted. High levels of wear result in leaks, which may require intervention on the part of the operator and can lead to apparatus down times. Furthermore, the fixedly set spring has difficulty reacting to thermal changes or positioning tolerances of the needle with the required degree of accuracy.
It is an object of the invention to achieve a higher accuracy of portioning with a needle feeder; in this context, it would be advantageous to achieve a portioning accuracy of ±50 mg or even a higher accuracy, however, without being forced to accept significantly increased wear or inaccurate positioning of the needle in its seat as well as resulting inaccurate portioning.